Saliva cortisol in school children after acute physical exercise

We investigated if 12 min of high-intensity exercise performed within a regular school break lead to an increase in cortisol levels in primary school students. 53 students of a 4th grade (9-10 years of age) were randomly assigned to an experimental (EG) and a control group (CG). Saliva collection took place after a normal school lesson (pre-test) and after 12 min of intensive exercise in a defined heart rate (HR) interval (EG, n = 32) and control condition (movie watching) (CG, n = 21), respectively (post-test). Saliva was analyzed for cortisol. We observed a significant group by test interaction indicating a different pre-to-post-test development for EG as compared to CG. The interaction effect, however, was caused by an attenuated cortisol concentration in the control group. We argue that the control condition, in which the students watched a joyful movie, acted as a distractor, which led to a reduction of general school stress.